The Cassegrain reflector(telescope) was designed by French engineer Laurent Cassegrain to compensate for the shortcomings of the Newtonian telescope.
Light reflected by the concave mirror is incident on the convex mirror. Focus is created only after reflection by the convex mirror. This unique construction enables long focal lengths in a short body.
Cassegrain reflectors are lightweight compared to other telescopes. In addition, there is an advantage that chromatic aberration is small.
The figure above shows how a light beam entering at an angle of 1˚ is bent at about 5˚. So the magnification of this telescope is 5.